Device for detecting a transport mishap of a copy paper in a reproducing apparatus

ABSTRACT

In a reproducing apparatus, a delay timer operates an alarm after the lapse of a predetermined period during which a copy paper fails to pass a point in its travel path through the machine. This timer is placed in the operating condition by a signal which is generated when the transfer drum begins to rotate. When the copy paper has been transported normally within a particular time, the operation mode is released. However, when the copy paper is not discharged owing to the occurrence of a paper jam after a predetermined time has elapsed, the timer is caused to operate an alarm to indicate the occurrence of the paper jam. For apparatus wherein the reproduction cycle is shorter than the transportation time and a series of copies are to be made, three delay timers with a system of associated relays are presented to detect a paper jam at any point in the cycle.

United States Patent [1 1 [111 3,833,896 Suzuki Sept. 3, 1974 DEVICE FOR DETECTING TRANSPORT Primary ExaminerGlen R. Swann, III

MISHAP OF A COPY PAPER IN A REPRODUCING APPARATUS Inventor:

Foreign Application Priority Data Dec. 28, 1971 Japan 46-373 US. Cl. 340/259, 271/258 Int. Cl. G08b 21/00 Field of Search 340/259, 309.1, 421;

References Cited UNITED STATES PATENTS Lundin et al. 340/259 Ziehm 271/57 Sauder 340/259 Attorney, Agent, or Firm--Cooper, Dunham, Clark, Griffin & Moran I [57 ABSTRACT In a reproducing apparatus, a delay timer operates an alarm after the lapse of a predetermined period during which a copy paper fails to pass a point in its travel path through the machine. This timer is placed in the operating condition by a signal which is generated when the transfer drum begins to rotate. When the copy paper has been transported normally within a particular time, the operation mode is released. However, when the copypaper is not discharged owing to the occurrence of a paper jam after a predetermined time has elapsed, the timer is caused to operate an alarm to indicate the occurrence of the paper jam. For apparatus wherein the reproduction cycle is shorter than the transportation time and a series of copies are to be made, three delay timers with a system of associated relays are presented to detect a paper jam at any point in the cycle.

5 Claims, 3 Drawing Figures I RA8-2 l RA4-3 V RA3-3 P RAs-z RA Ll RA4-2 RAY'I I RAs-z E0 RA4-r g as a PAIENIE SEP 3mm SNEEI 2 0F 3 Nam dm .3

PATENIEDSU 3 91 3.833.896

SHEET 30f 3 Fig. 3

PAPER CARRY 1st SHEET 2 SHEET 3rd v THVHNG fil i DEVICE FOR DETECTING A TRANSPORT MISHAP OF A COPY PAPER IN A REPRODUCING APPARATUS BACKGROUND OF THE INVENTION The present invention relates to a reproducing apparatus and in particular toa device for detecting a transport mishapof a copy paper in a reproducing apparatus using a transfer drum.

When a reproducing apparatus is operated for making a copy, there is in some cases an occasion wherein no copy paper is fed to a predetermined position, such as the discharge position, after a predetermined time has passed during which a copying operation should be effected following a signal indicating the supply of a copy paper for the operation. This may result from a mechanical mishap in the transport path of the copy paper, which may be due to the characteristics of the copy paper per se and the like. The condition wherein a copy paper has fallen into a mishap in a transport path will be generally called a paper jam.

In reproducing apparatus, using a transfer drum, when the transfer drum rotates one revolution, the steps of charging, exposure and development are effected and the developed toner images are transferred onto a copy paper. This is the so-called one cycle reproducing process and one copy is formed by these operations. When a plurality of copies are desired to be made, a repeat mechanism is set to a desired number of copies and the transfer drum 1 rotates the desired number of rotations to form a desired number of cop- 1es.

In a reproducing apparatus of such construction, various constructional parts must be arranged around the transfer drum in order to make the apparatus compact. Therefore, the relation between a mechanism for rotating and driving the transfer drum and a drive mechanism for transporting a copy paper becomes complicated. Particularly, the time for carrying out one cycle of the reproduction process, that is, the time during whch the transfer drum 1 rotates one revolution, may be made shorter than the time between the start of feeding a copy paper and the discharge of the reproduced paper. In other words, the copy paper will be still under transportation in the reproducing apparatus when the transfer drum has made one revolution. Further, there is a predetermined time relation between the beginning of the reproduction process and the beginning of feeding the copy paper, such that the rotation of the transfer drum begins simultaneously with the feed of a copy paper. Thus in the case of reproducing a plurality of copies, the next copy paper is fed into a transfer positionin the apparatus while the preceding transferred copy paper is still under transportation.

Therefore, a problem arises when the preceeding transferred copy paper causes a paper jam. That is, in the above-mentioned reproducing apparatus, copy papers are successively fed into the reproducing apparatus, although a paper jam has occurred to stop the advance of the preceding transferred copy paper.

SUMMARY OF THE INVENTION The present invention is intended to overcome such a drawback, that is, when a paper jam has occurred, the paper jam is detected by a timer means and simultaneously an alarm device is operated in order to stop the feed of the next copy paper. In the above-mentioned reproducing apparatus, for example, the time during which a transfer drum makes one revolution is about 4 seconds. However, the transport time of the copy paper during reproduction by this transfer drum is about 4.7 seconds. Therefore, the transport time of the copy paper is 0.7 second longer than the revolution time of the transfer drum. The difference between the transfer drum revolution time and the transport time of the reproducible copy paper is due to the comparable sizes of the drum copy paper and is 4.7 seconds at most. Accordingly, in the present invention, a delay timer which operates after a lapse of 5 seconds is used in consideration of the longest second time of 4.7 seconds. This timer is put in the operating condition bya signal which is generated when the transfer drum 1 begins to rotate. When the copy paper has been transported normally during a time less than 4.7 seconds, the operation mode is released. However, when the copy paper is not discharged owing to the occurrence of a paper jam after the time of five seconds has elapsed, the timer is caused to operate to indicate, such as by an alarm the occurrence of the paper jam. In such a way, the paper jam is detected through a timer means. Further, the present invention consists in providing a pair of time delay timers, one of which detects the paper jam of odd numbered copy papers and the others detects that of even numbered papers on the basis of the fact that a copy paper is still under transportation in the apparatus when the copy drum has completed one revolution and putting the delay timer detecting the paper jam of even numbered copy papers in an operating condition by transferring the signal generated at the starting of the revolution of the transfer drum 1 to another source of signal through a relay in the case of even numbered copy papers.

For better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a partial schematic view of a transfer type reproducing apparatus incorporating the present invention and;

FIG. 2 is a circuit diagram illustrating the electrical circuit in accordance with the present invention;

FIG. 3 is a time sequence diagram illustrating the op eration of the electrical circuit shown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION Firstly, the mechanical causes for the occurrence of the paper jam will be described in further detail. As shown in FIG. 1, in an electrophotographic reproducing apparatus using a transfer drum 1, made, for example of selenium, when the drum 1 rotates one revolution, toner images are formed on the surface of the drum through the steps of charging, exposure and transfer. A copy paper 4 which is fed out through a pair of feed rollers 2a and 2b and a pair of drawing out rollers 3a and 3b makes contact with a surface portion of this drum 1 and at the contact point a transfer voltage is applied through a transfer charger 5. The transferred copy paper is further fed out and its leading end collides with a separating finger 6, whose leading end is dropped into a slot la of the transfer drum 1. Then the finger 6 is moved to the dotted-line position, and the copy paper is separated from the drum 1 and fed out onto a transport belt 7.

The transport belt 7 is entrained over a plurality of transport rollers 8a and 8d and feeds out the transferred copy paper to a discharge opening. In a reproducing apparatus of such construction, when the position of the separating finger 6 is mechanically distorted for some reason, the normal separation of the copy paper is not effected and the transfer drum 1 becomes wrapped with the copy paper or the copy paper advances passing the vicinity of the finger 6 in the direction of an arrow A without colliding against the finger 6 and enters into another machine part. Further, as this transfer type reproducing apparatus may be used in the transfer of any kind of copy paper, the conditions of transport and separation change depending upon the nature of the paper used as a copy paper. That is, as the so-called knee strength of a paper is different due to the kind of paper, the conditions of transport and separation also change depending upon the kind of a paper. Further, such elements as the temperature, humidity, electrostatic phenomena and the like also have an effeet, as well as the nature of the paper per se, and sometimes becomes a cause of bending and the conditions wherein the separation and transport of the paper hecomes impossible may occur. When such a paper jam condition has occurred, the transport of the next copy paper is prevented.

Now the present invention will be explained with reference to the preferred embodiment shown in FIG. 2. FIG. 2 is an electric circuit diagram of the apparatus of the present invention. Across the terminals of a DC source E, there are connected a system of timers and relays in various parallel circuit legs in combinations as follows. The leftmost leg consists of switching contacts Tla, T2a and T3a of respective time delay timers T1, T2 and T3, whose operation will be explained in greater detail later. One terminal b of contact T3a is connected to a paper start switch PS, which closes at the instant when the transfer drum 1 begins to rotate to generate a pulsive signal for notifying the beginning of a reproducing operation. Switch PS is connected to a terminal Eb of source E through a relay RAl. Each switching contact Tla, T2a or T3a switches from its terminal b to its terminal when its respective timer T1, T2 or T3 is operated. The terminal c of each timer is connected in common to the terminal Eb of the power source E through a crime CI-I which provides an alarm sound when activated. Further, across the terminals of relays RAl, there is connected a solenoid SOL which when activated causes the drawout rollers 3a and 3b to be driven for a while in order to feed a copy paper.

In the next leg across the terminals of the DC source E, there are connected in series a normally closed type contact RAl-l of the relay RAl, normally closed type contact RA2-2 of relay RA2, and a relay RA3 with a parallel leg containing a normally closed type contact RA1-2 of the relay RA], and the relay RA2. The above-mentioned contacts RAl-l and RAl-Z are interlocked so that the contact RAl-l opens when the contact RA1-2 is closed.

In a further leg, across the power source E, there are connected a relay RAS in series with a change-over switch MS for detecting the transfer mishap. More particularly, a moving arm MSo of this switch MS is connected to the terminal Ea of the power source E and the relay RAS is connected between its fixed terminal b and the terminal Eb of the power source. Also, to the fixed terminal aof this switch MS, is connected the relay RA2 via its normally opened type contact RA2-l. Further, change-over switch MS is positioned at the discharge opening of the reproducing apparatus as shown in FIG. 1 so that its moving arm MSo will be switched fromthe fixed terminal a to the terminal b by engagement with the leading end of the transported copy paper. Therefore, the moving arm M is switched to the fixed terminal b when a copy paper to be discharged pushes it while passing.

Referring to FIG. 2 again, it will be seen that between the fixed terminal b of switch MS and the terminal Eb of the power source, there is connected timer T3 consisting of a timer delay relay. This timer T3 causes current to flow when the change-over switch MS is switch to the terminal b and is made to operate for instance 5 seconds after the beginning of the current flow. When timer T3 is operated, the contact T3a is switched from its terminal b to terminal c. Therefore, when switch MS is changed over, current flows through the chime CH, actuating the chime alarm. Thus, timer T3 serves to provide an alarm whenthe moving arm MSo does not return to its original position, for any reason, after it has changed over to the fixed terminal b and the copy paper has been discharged through the discharge openmg.

In another leg across both ends of the power source E, there is connected in series the normally opened contact RA4-3 of RA4 and the normally opened contact RA7-l of relay RA7-. Also, between the junction of the contact RA7-1 and the relay RA7, and the fixed terminal a of the switch MS, there is connected normally closed contact RA5-3 of relay RAS and normally opened contact RA6-2 of relay RA6 in series. Between the junction of the relay RA2 and the contact RA2-1, and the junction of the relay RA3 and the contact RA2-2, there is connected normally opened contact RA3-l of the relay RA3 through a diode D. Further, a parallel circuit containing normally opened contacts RA7-3 and RA8-3 is connected between the fixed terminal a of the switch MS and the normally opened contact RAl-2 of the relay RA2.

A further leg is connected between the junction of the contacts RA4-3 and RA7-1, and the terminal Eb of the power source, and contains in series normally opened contact RAS-l of relay RAS and the relay RA6, and in parallel across both ends of the contact RAS-l, there is connected the normally opened contact RA6-l of the relay RA6. Further, across both ends of the power source E, there is connected a series circuit of normally closed contact RA8-l of relay RA8, normally opened contact RA3-3 of the relay RA3, the normally opened contact RAl-3 of the relay RAl, and the relay RA4. In parallel across the ends of the contacts RA3-3 and RAl-3, is connected normally opened contact RA4-1 of the relay RA4.

In the remaining legs, across the ends of the power source E, there are connected in series normally opened contact RA7-2 of the relay RA7, normally opened contact RA5-2 of the relay RAS, and the relay RAS, with normally opened contact RA8-2 of the relay RA8 connected in parallel across the normally opened contact RA7-2; normally opened contact RA3-2 of the relay RA3 and a timer Tl consisting of a time delay relay; and normally opened contact RA4-2 of the relay RA4 and timer T2 consisting of a time delay relay. The

timer Tl detects paper jams caused by the odd numbered copy papers and the timer T2 detects those caused by the even numbered papers. Finally all the relays and timers are provided with by-pass diodes as shown in FIG. 2.

The above-described electric circuitry constitutes the detecting device of the present invention. Now the operation of the circuit will be explained with reference to the time sequence diagram shown in FIG. 3. When the'copy drum 1 begins to rotate in order to make a copy, the switch PS is closed by the starting of the drum. Whenthis switch PS is closed, the relay RAl and the solenoid SOL are actuated. Upon actuation of the solenoid SOL, the drawing out rollers 3a and 3B are driven and the transport of a copy paper 3b begun; while upon actuation of relay RAl, simultaneously, the contact RAl-l is opened, the contact RA1-2 is closed, and the contact RAl-3 is also closed. When the contact RAl-Z is closed, the relay RA2 operates, owing to the current flow therethrough, and consequently, the contacts RA2-l and RA2-2 are closed. If when the contact RA2- 1 is closed, the moving arm MS of the switch MS is in contact with its fixed terminal a, the contact RA2-l and arm MS0 will afford another current. path to the relay RA2.

The switch PS is such that it is merely momentarily closed, so that the relay RAl conducts current only momentarily and the contacts RAl-l and RAl-2 are actuated for just a short time whereupon the contact RAl-l is again closed and the contact RA1-2 is opened. However, as the contact RA2-l is still closed, the relay RA2 continues to conduct. Further, when the contact RAl -l is closed, the relay RA3 is actuated since the contact RA2-2' is already closed. When this relay RA3is operated, the contacts RA3-1, RA3-2 and RA3-3 are closed. The closing of contact RA3-l creates another current path to relay RA3. When the contact RA3-2 is closed, the timer Tl begins to conduct current. The timer T1 is set to be actuated for a predetermined period, for instance 5 seconds. In this circuit condition, he detecting device for a paper jam is now operative. Therefore, when a paper jam has occurred. under'this condition and the transport of a. copy paper is stopped, the copy paper will not be discharged evenafter the predetermined period for instance 5 seconds haspassed. At this time, the timer Tl operates the contact Tla, which is switched from the fixed terminal b to the terminal c. When this switching occurs, the chimeCI-I is operated. to. give an alarm notifying that the paper jam has occurred.

On the other hand, when the transportv operation of a copy paper is effectednorrnally, the copy paper will be discharged. within the predetermined 5' second period from the discharge opening and the leading end of the copy paperwill engageand change over the switch arm MSO from the fixed terminal a to the terminal b. When the changeover is'effected, the relay RAS' is operated to close the contacts RAS-l and RAS-Z. and open the contact R'A5-3.. Further, as the. circuit continuitythrough the relays RA2 andv RA3 is interrupted simultaneously with this operation, each contact of both relays RA2 and RA3 is returnedto its original position asrshown in. the time sequence diagram of FIG. 3. Therefore, contact RA3-2 is openediand the'detecting condition of the timer T1 is released. However, as the timer T3 is actuated to. conduct current. upon the switching of arm MSO to terminal b, the detecting action is transferred to timer T3 and continues until the rear end of the copy paper is fully discharged. Accordingly when he transport of the copy paper is stopped in this condition, the timer T3 which may be set to operate for 5 seconds, when changes over the contact T3a from the fixed terminal b to the terminal 0. Therefore, this extraordinary condition may be alarmed through the chime CH. The detecting operation continues in this way. However, when an extraordinary condition does not occur and the rear end of copy paper is discharged, the switch arm MS0 is changed over to the contact a to interrupt the circuit continuity through the relay RAS and the timer T3, and all the contacts are reset to their original condition.

The above is the operation when one copy is to be made. However, when the apparatus is set for a repeating operation, as will be seen in FIG. 3, the switch MS is in the position of contact a when the second copy start signal is initiated. Therefore, the copy start signal for the 2nd sheet is generated by the swtich PS while the relays RA2 and RA3 are still in operation since the leading edge of the 1st sheet has not yet changed the position of switch MS. When this signal is generated momentarily, the relay RAl operates to open contact RAl-l and to close contacts RAl-2 and RAl-3. As the contact RA3-3 is' already closed, the relay RA4 operates to close the contacts RA4-1, RA4-2 and RA4-3 when the contact RAl-3 is closed. With the contact RA4-1 closed, the relay RA4 will continue to operate even through the contact RA1-3 is then opened. Further, with the contact RA4-2 closed, the timer T2 is caused to begin operation and the detecting condition for the paper jam of the 2nd sheet is now operative. Then, when the switch MS is engaged and changed over to the terminal b by the leading edge of the 1st sheet, the timer T1 becomes deactivated and the timer T3 is changed over to the detecting condition in the manner mentioned above. Also, when the switch MS is changed over to the terminal b, the contacts RAS-l and RA5-2 are closed and the contact RA5-3 is opened because the relay RAS is operated. The closing of contact RAS-l causes relay RA6 to operate resulting in the reaction of another current flow path to itself by the closure of the contact RAG-l, and also closing the cntact RA6-2. When the discharge of the 1st sheet is normally effected, the switch MS is changed back to the terminal a deactivating timer T3. When this switching is effected, the circuit continuity to the relay RAS is interrupted to open the contacts RA5-l,RA5-2 and to close the contact RA5-3. As the contact RA6-2 is already closed, the closing of contact RA5-3 causes relay RA7 to operate closing the contacts RA7-1, RA7-2 and RA7-3. The closing of contact RA7-l. creates another current path to relay RA7.

At this time, the timer T2 only is in the condition. for detecting the paper jam of the 2nd sheet. If the paper jam condition occursfor the 2nd sheet,.after aipredetermined lapse of time, the timer T2 operates to change over the contact T2a from the terminal b to the terminal c so as to ring chime CH for notifying that the 2nd sheet has induced the paper jam. While the 2nd sheet is being transported normally, the reproductionv of the third copy is begun through the repeat mechanism. As the 3rd sheet isan odd numbered copy,.the relays RA2 and- RA3 operate as in the case of the first copy.

The subsequent operations of the circuit is the same as for the first copy. The transport of the third. sheet starts the timer T1 in the operating condition. When he leading edge of the 2nd sheet arrives at the switch MS thereafter, the switch arm M50 is changed over from the termial a to the terminal b. At this point, since contact RA7-3 is closed, relay RA-2 and in turn relay RA3 will remain operative, so that contact RA3-2 remains closed and timer T1 continues its operation. The tim r T3 is also actuated by the changeover to begin the detecting operation until the second copy paper is discharged, and the relay RA5 operates again to close the contacts RAS-l, RA5-2, and to open the contact RAS- 3. When the contact RA5-2 is closed, since contact RA7-2 is already closed, the elay RA8 operates to open the contact RA8-l. Current to the relay RA4 is thus interrupted causing contact RA4-2 to open deactivating timer T2. The contact RA8-2 is closed to create another current path to relay RA8. When the relay RA4 becomes inactive, the contacts RA4-1, RA4-2 and RA4-'3 are opened. The opening of contact RA4-3 causes the operation of relays RA6 and RA7 to also be interrupted. Although contact the terminal timer relay RA7-3 now opens, relays RA2 and RA3 continue to operatesince contact RA8-3 has been closed upon the actuation of relay RA8. Therefore, as shown in FIG. 3, at this point, the relays RA2, RA3, RAS and RA8 are in operating condition. The timers T1 and T3 are thus operating to detect any paper jam of the second and third copy papers respectively. After the second copy paper has been normally discharged, the next or fourth paper, that is, another even numbered paper is transported activating relay RA4 to operate the timer T2 and deactivating relay RA3 cutting off timer T1. The operation of each relay and the changeover of the switch MS for these third and fourth copy papers are then similar to those for the first and second copy papers.

As mentioned above, in accordance with the present invention, it is possible to effect the detection of paper jams in'reproduction apparatus successfully using time delay timers. Further, by effecting the detection of odd numbered and even numbered copy papers through the timers T1 and T2 respectively, it is possible to overcome the problem created by the fact that the time during which the transfer drum makes one revolution is shorter than the time during which a copy paper to be copied is transported through a reproduction process.

Although, in the above-mentioned embodiment, the operations of timers T1, T2 and T3 causes a chime to give an alarm for notifying an operator of the occurrence of a paper jam, the use of a chime is not necessary, but rather a buzzer, a lamp or another indicating device may also be used. Further, the paper supply mechanism may be inactivated by the alarm and any suitable means may be applied for this procedure.

Thus it is possible to' avoid waste of the copy papers after a paper jam has occurred. Further, the present invention may be applied to any reproducing apparatus wherein the time for one cycle of a reproducing process is shorter than the time between the start of feeding a copy paper and the discharge of the reproduced paper and the beginning time of the reproducing steps has a predetermined time relation with the beginning time of transporting a copy paper.

While the invention has been described with reference to the structure disclosed herein it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements defined in the following claims.

What is claimed is:

1. In a reproducing apparatus wherein the time for one cycle of the reproducing process is shorter than the time of transportation between the start of feeding a copy paper and the discharge of the reproduced paper and the beginning time of the reproducing process has a predetermined time relation with the beginning time of transporting a copy paper, a device for detecting a transport mishap of a copy paper comprising a circuit including:

a. a transport mishap indicator means;

b. detector means for switching from a normal condition to an alternate condition during the passage of a copy paper thereby;

c. relay means activated in response to the initiation of the reproducing process; and

d. timer means activated to operate for a predetermined period of time in response to the activation of said relay means, for operating said indicator means if said detector means after the lapse of the predetermined period of time has not been switched to its alternate condition;

c. said timer means comprising a first time delay timer and said relay means comprising:

i. a first relay momentarily activated upon initiation of each reproduction process;

ii. a second relay activated in response to the activation of said first relay; and

iii. a third relay activated in response to the activation of said second relay, for operating said first time delay timer, said second and third relays being deactivated by the switching of said detector means to its alternate condition.

2. A device as in claim 1 further comprising second timer means activated to operate for a second predetermined period of time in response to the switching of said detector means to its alternate condition, for operating said indicator means if said detector means after the lapse of the second predetermined period of time has not been switched to its normal condition.

3. A device as in claim 1 further comprising a second time delay timer and a fourth relay, activated in response to the activation of said first relay when said detector means is in its normal condition, for operating said second time delay timer.

4. A device as in claim 3, further comprising a fifth relay activated when said detector means is in its alternate condition; a sixth relay activated in response to the activation of said fifth relay; and a seventh relay activated in response to the deactivation of said fifth relay after the activation of said sixth relay, for subsequently maintaining the operation of said second relay and said third relay upon the return of said detector means to its alternate condition following the activation of said first relay.

5. A device as in claim 4, further comprising an eighth relay activated in response to the concurrent activation of said seventh relay and said fifth relay for deactivating said fourth relay. 

1. In a reproducing apparatus wherein the time for one cycle of the reproducing process is shorter than the time of transportation between the start of feeding a copy paper and the discharge of the reproduced paper and the beginning time of the reproducing process has a predetermined time relation with the beginning time of transporting a copy paper, a device for detecting a transport mishap of a copy paper comprising a circuit including: a. a transport mishap indicator means; b. detector means for switching from a normal condition to an alternate condition during the passage of a copy paper thereby; c. relay means activated in response to the initiation of the reproducing process; and d. timer means activated to operate for a predetermined period of time in response to the activation of said relay means, for operating said indicator means if said detector means after the lapse of the predetermined period of time has not been switched to its alternate condition; e. said timer means comprising a first time delay timer and said relay means comprising: i. a first relay momentarily activated upon initiation of each reproduction process; ii. a second relay activated in response to the activation of said first relay; and iii. a third relay activated in response to the activation of said second relay, for operating said first time delay timer, said second and third relays being deactivated by the switching of said detector means to its alternate condition.
 2. A device as in claim 1 further comprising second timer means activated to operate for a second predetermined period of time in response to the switching of said detector means to its alternate coNdition, for operating said indicator means if said detector means after the lapse of the second predetermined period of time has not been switched to its normal condition.
 3. A device as in claim 1 further comprising a second time delay timer and a fourth relay, activated in response to the activation of said first relay when said detector means is in its normal condition, for operating said second time delay timer.
 4. A device as in claim 3, further comprising a fifth relay activated when said detector means is in its alternate condition; a sixth relay activated in response to the activation of said fifth relay; and a seventh relay activated in response to the deactivation of said fifth relay after the activation of said sixth relay, for subsequently maintaining the operation of said second relay and said third relay upon the return of said detector means to its alternate condition following the activation of said first relay.
 5. A device as in claim 4, further comprising an eighth relay activated in response to the concurrent activation of said seventh relay and said fifth relay for deactivating said fourth relay. 